Abstract
BackgroundHydrogen gas (H2) is hypothesised to play a role in plants that are coping with stresses by regulating signal transduction and gene expression. Although the beneficial role of H2 in plant tolerance to cadmium (Cd) has been investigated previously, the corresponding mechanism has not been elucidated. In this report, the transcriptomes of alfalfa seedling roots under Cd and/or hydrogen-rich water (HRW) treatment were first analysed. Then, the sulfur metabolism pathways were focused on and further investigated by pharmacological and genetic approaches.ResultsA total of 1968 differentially expressed genes (DEGs) in alfalfa seedling roots under Cd and/or HRW treatment were identified by RNA-Seq. The DEGs were classified into many clusters, including glutathione (GSH) metabolism, oxidative stress, and ATP-binding cassette (ABC) transporters. The results validated by RT-qPCR showed that the levels of relevant genes involved in sulfur metabolism were enhanced by HRW under Cd treatment, especially the genes involved in (homo)glutathione metabolism. Additional experiments carried out with a glutathione synthesis inhibitor and Arabidopsis thaliana cad2–1 mutant plants suggested the prominent role of glutathione in HRW-induced Cd tolerance. These results were in accordance with the effects of HRW on the contents of (homo)glutathione and (homo)phytochelatins and in alleviating oxidative stress under Cd stress. In addition, the HRW-induced alleviation of Cd toxicity might also be caused by a decrease in available Cd in seedling roots, achieved through ABC transporter-mediated secretion.ConclusionsTaken together, the results of our study indicate that H2 regulated the expression of genes relevant to sulfur and glutathione metabolism and enhanced glutathione metabolism which resulted in Cd tolerance by activating antioxidation and Cd chelation. These results may help to elucidate the mechanism governing H2-induced Cd tolerance in alfalfa.
Highlights
Hydrogen gas (H2) is hypothesised to play a role in plants that are coping with stresses by regulating signal transduction and gene expression
As detected by gas chromatography, endogenous molecular hydrogen (H2) in alfalfa seedling roots was increased by 84.09% after 12 h of Cd stress, and a higher H2 content was found after the administration of hydrogen-rich water (HRW) followed by Cd exposure (Additional file 1: Figure S1)
We sequenced four groups of complementary DNA libraries, Sample 1 (12 h in 1/4 Hoagland’s solution changed to fresh 1/4 Hoagland’s solution for another 12 h, control samples (Con) → Con); Sample 2 (12 h in 1/4 Hoagland’s solution changed to 12 h of Cd treatment in 1/4 Hoagland’s solution, Con → Cd); Sample 3; and Sample 4, and generated 60,723, 124 sequence reads encompassing 9.24 Gb of sequence data (Additional file 2: Table S1)
Summary
Hydrogen gas (H2) is hypothesised to play a role in plants that are coping with stresses by regulating signal transduction and gene expression. The transcriptomes of alfalfa seedling roots under Cd and/or hydrogen-rich water (HRW) treatment were first analysed. Hydrogen gas (H2) has recently emerged as a molecule that plays physical regulatory roles in plants and animal models. The mechanism governing H2 production in higher plants remains elusive, the bioregulatory role of H2 has been revealed in recent years. H2 was found to play roles in root formation by interacting with the nitric oxide and haem oxygenase-1/carbon monoxide pathways [8, 9]. Accumulating reports have shown that H2 production is elevated in many plant species under abiotic stresses, such as paraquat, NaCl, high light, UV-A, UV-B, and heavy metal stresses, and H2 can further act as a regulator in plants coping with abiotic stresses [5, 10,11,12,13,14,15,16,17]
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